The invention relates to measuring a physiological characteristic of a patient, and particularly, to an electrocardiograph including a method and apparatus for identifying the relative position of the electrodes connected to the patient.
It is commonly known that ten electrodes and ten leadwires are needed to record and present what is commonly referred to as a twelve lead electrocardiogram (ECG), i.e., a group of twelve signals representing twelve different "views" of the electrical activity in the patient's heart. For standard or resting ECG electrode placement, one electrode is attached to each of the four body limbs at the right wrist, left wrist, right ankle, and left ankle. Additionally, six electrodes are attached to the chest over the heart. The ten electrodes connect via several resistor networks to enough amplifiers to record twelve channels of ECG. The twelve leads (i.e., signals) are generally split into two groups comprising the frontal plane and the horizontal plane. The frontal plane leads (I, II, III, aVr, aVl, aVf) are variously referred to as limb leads, Einthoven leads, or bipolar leads. The horizontal plane leads (v1, v2, v3, v4, v5, v6) are likewise variously referred to as precordial leads, chest leads, or unipolar leads.
Accurate placement of the electrodes on the patient's body surface is required to record a useful ECG using an electrocardiograph or patient monitor. The ideal placement of electrodes for a standard ECG is well defined and accepted within the medical industry. However, routine correct placement of the electrodes in the clinical environment is difficult to achieve for several reasons. First, nurses and ECG technicians are frequently not adequately trained or are too inexperienced to accurately locate the attachment points. Moreover, individual physical characteristics vary widely from patient-to-patient. These variations lead to misinterpretation of the "anatomical guideposts" used to locate the proper attachment points. Additionally, patients sometimes have wounds or bandages that preclude access to the patient's body surface at the proper attachment points. Also, attachment of the electrodes to an ECG machine is often accomplished using long individual ECG leadwires. Even if the electrodes are accurately placed on the patient, the leadwires connecting them to the electrocardiograph may be crossed such that signals are switched at the instrument.
Many inventors have attempted to solve the problem of electrode connection to the chest. Numerous belts, pads, vests, harnesses and strip electrodes have been developed that place a multitude of electrodes into an ordered arrangement to facilitate the attachment of the leads to the patient and eliminate the possibility of some types of attachment errors. In general, these inventions attempt to fix the six horizontal electrodes in relation to each other while adapting to different patient sizes. None of these teachings address the issue of placement of the limb electrodes. Moreover, the location of the horizontal lead electrodes may still not be at the proper anatomical positions.
In some ECG applications the patient must be free to move. Thus, it becomes inconvenient or impossible to place the electrodes on the wrists and ankles. Applications where the patient must be free to move include long term recordings, known as holter; ambulatory patient monitoring, such as telemetry monitoring; and exercise testing on treadmills or bicycles, known as stress testing. In these tests, the wrist and ankle electrode positions are unacceptable for electrode placement due to inconvenience, increased danger of tangling of the lead wires, and increased noise from limbs in motion. Generally, in each of these ECG applications the limb electrodes are moved onto the torso and placed near the shoulders and hips. The Mason-Likar system is one variation of electrode placement on the torso. Twelve-lead bedside monitoring also requires placement of the electrodes on the torso. In each of the systems for alternative electrode placement, useful ECG data is obtained, but the data differs significantly from standard EGC data. Important differences in amplitudes and waveforms occur between standard ECGs and alternative electrode placement ECGs.
Due to tile differences between data obtained from standard ECGs and alternative electrode placement ECGs, a complication in ECG analysis arises when all ECG test results, regardless of the type of electrode placement, are stored in the same hospital storage system. The same patient may have ECG data stored on the hospital system for a standard ECG and an ECG obtained during a stress test. If no explanation is given for the differences in the data, cardiologists and hospital technicians may be confused when both sets of ECG data are viewed together.